The present invention relates to improvements in a diffuser of a centrifugal compressor used in a centrifugal refrigerator, an air compressor, apparatus for sending natural gas under pressure, or the like.
A centrifugal compressor generally includes a diffuser for reducing the speed of a fluid disposed downstream of the outlet side of an impeller to convert the dynamic energy into a static pressure, and a scroll disposed as connected to the diffuser. The diffuser is generally formed by a pair of parallel lateral walls.
To improve the efficiency of the diffuser in a centrifugal compressor, Japanese Unexamined Patent Publication 156299/1980 proposes a diffuser in which the width of the inlet portion is narrowed in order to prevent the fluid from reversely flowing at the diffuser inlet portion, thereby to reduce the loss due to the fluid eddy.
Even though the width of the inlet portion is narrowed, the flow separation may be restrained only to a limited extent and a portion of the flow may be arranged. In particular, when the width of the inlet portion is narrowed too much, the conformity of the impeller with the diffuser is lost to increase the loss. This may not only impose restrictions on improvements in partial load efficiency, but also induce decrease in both rated efficiency and maximum flow rate. Further, even though the width of the inlet portion is narrowed, the surge line cannot be heightened.